Spray dampening system for lithographic offset printing presses



Aug. 30, 1955 J. K. MARTIN 2,

SPRAY DAMPENING SYSTEM FOR LITHOGRAPHIC OFFSET PRINTING PRESSES Filed Nov. 2, 1955 2 Sheets-Sheet l Aug. 30. 1 J. K. MARTIN SPRAY DAMPENING SYSTEM FOR LITHOGRAPHIC OFFSET PRINTING PRESSES Filed Nov. 2, 1953 2 Sheets-Sheet 2 United States Patent Ofitice 2,716,380 Patented Aug. 30, 1955 SPRAY DAMPENING SYSTEM FOR LITHO- GRAPHIC OFFSET PRINTING PRESSES James K. Martin, Chicago, Ill., assignor to Lithographic Technical Foundation Application November 2, 1953, Serial No. 389,740

6 Claims. (Cl. 101-147) This invention relates to spray dampening equipment for lithographic offset presses whereby, as is customary in such printing, the surfaces of the printing plates are dampened before the printing ink is applied thereto in order to prevent adhesion of the ink to those parts of such surfaces on which no printing image appears.

Various types of dampening devices for this purpose have been employed in the past but they have all had faults or shortcomings of one sort or another and it is the general purpose of the present invention to provide a spray dampening system which is superior in efficiency and operating results to those that have heretofore been devised and which overcomes the principal difficulties that have been involved in their use.

One object of the invention is to provide a spray dampening system in which the amount of the spray can be automatically regulated with respect to the press speed.

Another object is to provide such a system in which the spray is automatically cut off at the cylinder gap.

A further object is to provide a spray dampener in which the spray is directed electrostatically to the plate cylinder only.

It is also an object of my invention to provide apparatus for the purpose stated in which the spray may be controlled around and across the cylinder.

An additional object is to provide a system of this character in which the chance of plugging of the spray devices is eliminated or greatly reduced.

Other objects and advantages of the invention will be evident from the following description, taken in connection with the accompanying drawings, in which:

Fig. l is a view, partly in horizontal section and partly in plan of an elongated container or chamber in which the spray medium is formed and from which it is directed to the printing cylinder between electrically charged metal plates, some of which are shown protruding from the chamber;

Fig. 2 is a cross-sectional view of the chamber and of a bank of the plates, taken substantially on the section line 22 in Fig. 1;

Fig. 3 is a detail sectional view, partly broken away, of

existing dampening systems, and prior attempts to over come them, will be referred to, since it is believed this will be helpful in understanding the problems involved and the ways in which they are solved by the present invention.

It has been foundin the use of the customary dampening rollers that they have a tendency to pick up ink and deposit scum on the printing plates; the over-all control of the moisture is dependent on the precision of the dampening rollers, which is difficult to maintain; specific control across the cylinder is dependent on conditions that are hard to reproduce and there has been no satisfactory method' of controlling the moisture around the cylinder; present methods require considerable makeready time to reach an equilibrium; the cloth coverings commonly used on the dampening rollers introduce lint which may cause printing imperfections; foreign matter, such as ink, may be transferred back to the reservoir, thus requiring, in some cases, frequent adjustments and filtering; and there has been no satisfactory way of automatically controlling the amount of moisture in .relatio to press speeds.

In attempting to overcome these difiiculties various schemes have been tried, falling generally into two categories, namely (1) those in which the plates are sprayed by a series of nozzles and (2) those in which the spray medium is introduced into a chamber running parallel to the plate cylinder and having a slot through which the spray is directed to the cylinder. Both schemes have been subject to the general objections that: no method is provided'to stop the spray at the cylinder gap, with the result that corrosion of the cylinder clamps becomes a.

problem; no method is provided to automatically control the volume of the spray with relation to'press speeds; there is no way to confine the spray to the plates, with the result that parts .of the press in close proximity to the plate cylinder, as well as the paper, are undesirably moistened; and-there is no method of controlling the spray around the cylinder, which is sometimes to be desired, as when a solid and a halftone are being run in'the same section around the cylinder. A further specific objection with respect to the first-mentioned of these schemes, namely the use of a multiplicity of spray nozzles, is that, since the sprays must be fine to avoid flooding the plate, plugging of the orifices becomes a problem. Another specific objection with respect to the secondmentioned of such schemes, namely, spraying from a slotted chamber, is that control across the cylinder is difiicult because shutting off one section'of the slot to stop delivery of the spray increases the pressure inside the chamber, thereby unduly increasing the amount of the spray in the open areas.

As hereinabove stated, it isthe purpose of my invention to solve these problems and overcome the above objections to prior and existing dampening systems by means of the system illustrated (more or less diagrammatically) in the above-described figures of the accompanying drawings.

Referring first to Figs. 1 and 2 of said drawings, the reference numeral 11 indicates an elongated container or chamber (of any desired but preferably cylindrical form) having a longitudinal opening 12 in one side thereof and having a series of spaced metal plates 13 extending through said opening and protruding a considerable distance therefrom, said' plates, as shown, being disposed in upwardly inclined arrangement with quite substantial space therebetween. The plates, which are made of suitable metal to receive an electrical charge, are arranged in a plurality of sets or banks lengthwise of the chamber, and the plates of each set are supported by bars 14 of suitable insulating material, so that the sets of plates are insulated from each other. Said bars 14 are recessed to receive the edges of the plates 13 and are suitably supported by the chamber 11. The means for attachment thereof are not shown in detail since any suitable devices for this purpose may be used, but supporting straps or brackets 15, the arms of which are riveted to the container 11 and one of the end bars 14, respectively, may be used, one thereof being shown in Fig. 2.

The container or chamber 11 is suitably supported adjacent a plate cylinder 16 of a printing press and, as shown in Fig. 1, is broken away centrally to indicate that it may be of any suitable length and arranged to carry any appropriate number of sets or banks of the plates 13 as varying press types and sizes may dictate. As shown in Fig. 1, the ends of the chamber 11 are closed by removable caps or closure members 17 which, as illustrated, are provided with screw-threaded portions 18 adapted to screw onto mating portions 19 on the body of the chamber.

For the purpose of introducing a charged spray or aerosol into the chamber 11, two atomizers 21 are shown in the chamber near the opposite ends thereof. They each comprise an air nozzle in the form of a block 22 having a conical chamber 23 therein connected. with an intake pipe 24 leading from a source of compressed air; and a liquid nozzle 25 connected with a pipe 26 leading from a reservoir (not shown) or other source of liquid, which may be water or a suitable liquid solution such as, for

example, ammonium bichromate. The air will normally be under pressure of, say, to pounds per square inch and the liquid may be fed by gravity to the atomizer. Between the air nozzle 22, 23 and the liquid nozzle a source of potential is provided and connected, as shown, by way of example, in the wiring diagram of Fig. 5. In this connection it should be noted that the container or chamber 11, 17 may be of insulating material, such as polyethylene, so that proper electrical connections, as shown in said Fig. 5, may be made to said nozzles.

The sprays emitted from the atomizers 21 are indicated at 27 and are preferably directed against the ends of the chamber from which the spray medium is diffused into the interior of the chamber. The atomizers thus operate on the principle of space chargers. It will be evident that other means of obtaining a charged spray could be employed if preferred.

A drain pipe 28 is provided, leading from the bottom of the chamber, as shown in Figs. 2 and 4 of the drawings.

The charged spray is forced by the pressure in the chamber out between the plates 13 and onto the printing element on the cylinder 16. An electrical charge is placed on these plates, its purpose being to either attract or repel the charged vapor particles so that a greater or less amount thereof will be precipitated as conditions require, and the volume of the spray reaching the plates on the printing cylinder thus controlled. Since the plates are arranged in a plurality of sets or segments lengthwise of the spray chamber the potential applied to the different sets of plates may be varied if desired and the quantity of the spray which is precipitated thus controlled across the cylinder.

The means for charging the plates of course could be varied to meet particular conditions, but one embodiment is shown for illustrative purposes in Fig. 5 of the drawings, in which a D. C. generator 29 is shown as being mechanically coupled to the drive motor 31 of the press, although it will be evident that it could be coupled to some other rotating element of the press if desired. The output of this generator is applied to the primary winding 32 of a saturable core reactor, generally indicated at 33, being connected thereto by wires 34 and 35. The secondary winding 36 of the reactor is connected in series, by wiring 37, with the primary winding 38 of a power transformer, generally indicated at 39, and with an A. C. power source, the lead to which is indicated by the numeral 41. The primary 38 of said power transformer 39 is also connected with the A. C. power source, by a lead 42. The output of the power generator 39 is applied to the spray control plates 13, one set of which is shown in said Fig. 5,

the arrows 43 indicating that it may be similarly applied to other sets or units as called for by the particular installation.

The output of the power transformer 39 may be applied to the control plates either directly or through a rectifier. In the embodiment shown, the secondary 44 of the transformer is connected by leads 45 and 46 with a rectifier 47 which, in turn, is connected by leads 43 and 49 with the plates, the atomizer or space charger 21 being interposed between these leads by means of wires 51 and 52.

Control of the spray is provided by means of a normally open switch 53 and a variable resistor 54 and specific unit control by a variable resistor 55 and a normally closed switch 56.

A normally open cam switch 57 (Figs. 4 and 5) is pro vided in one of the leads to the A. C. power source and is adapted to be operated by a cam 58 on the shaft 59 of the plate cylinder 16. Closing of this switch activates a relay 60 which closes the switch 53 and opens the switch 56 to cut off the spray at the cylinder gap. When said switch 57 is open so that no current is flowing through the relay 60, and with switch 53 open and the switch 56 closed (as they normally are), current is forced to go through the general control resistor 54 and the individual unit control resistor 55. Since these resistors limit the voltage reaching the plates 13, and the volume of the spray is in inverse order to such voltage, the proper amount of spray will be applied to the plate cylinder 16 when the above-described condition of the switches 57, 53 and 56 prevails. On the other hand, when the switch 57 is closed by the cam 58, current passes through the relay 60 and this causes the switch 53 to be closed and the switch 56 to be opened, thus taking the resistors 54 and 55 out of the circuit and allowing full voltage to be applied to the control plates 13, thereby stopping the spray. It will be evident that the cam 58 is so located with respect to the cylinder gap 50 (customarily provided for purposes of margin and of plate attachment) that the switch 57 will be periodically closed at such times as the cylinder gap is opposite the spraying device. In a normal installation the particle velocity and the dimensions and relationship of the plates may be such that the time for complete condensation of the spray on the plates will be on the order of one-half second. The cam 58 is so formed that the switch 57 will be closed a suificient time before the cylinder gap reaches a position opposite the spray area that the cut-off will take place at the right time.

The plates 13 are electrically connected together, the connections being shown at 61 and 62. As shown,'they are wired so that every other plate would have the same charge and those between would have an opposite charge, but, if desired, they could be wired so that all of the plates would have the same charge.

A fixed leak resistor 63 is, or may be, connected across the control plates 13, by wires 64 and 65, to insure a more uniform load and thus aid in securing proper control.

When the press speed increases, the volume of the spray should increase to provide adequate dampening of the plates. In the present system this result is accomplished since as the press speeds up the generator speed increases correspondingly. As it runs faster its D. C. voltage will increase. This increased voltage, when applied across the primary of the saturable core reactor 33, will increase the reactance, thereby decreasing the amount of A. C. voltage that can flow through the secondary 36 of the reactor. Since said secondary is in series with the primary winding 38 of the power transformer 39, the voltage output of the transformer will thereupon decrease, thus decreasing the voltage on the spray control plates 13. Since the amount of spray which gets through these plates is inverse to the voltage applied to the plates, an increase in the volume of the spray will thus be obtained.

From the foregoing description it will be apparent that I have not only thus provided a system whereby the amount of the spray will be automatically regulated with respect to press speed but one in which the various other objects hereinabove set forth are attained and in which the principal difliculties of systems heretofore used are overcome. It will also be evident, and is to be understood, that various changes and modifications in the above described illustrative embodiment of the invention may be made without departing from the principles of the invention or the scope of the appended claims.

I claim:

1. A spray dampening system for lithographic offset presses comprising: an elongated chamber arrangeable' in proximity to a printing cylinder adapted to carry a printing plate or medium to be dampened and having a lengthwise outlet slot therein opening toward said cylinder; means for providing in said chamber an electrically-charged dampening spray medium under pressure; a series of substantially parallel metal plates fixedly supported by the chamber and so disposed in relation to said slot that the spray medium must pass between them in moving from said chamber toward said cylinder; means for placing an electrical charge on said plates to cause precipitation of a controlled quantity of the charged particles of said dampening spray medium; means for placing an electrical charge on said spray medium; and means for varying the strength of the electrical charge of a given polarity on said plates with respect to the charge on said spray medium.

2. A spray dampening system for lithographic ofiset presses comprising: an elongated chamber arrangeable in proximity to a printing cylinder adapted to carry a printing plate or medium to be dampened and having an outlet opening therein opposite said cylinder, means for providing in said chamber an electrically-charged dampening spray medium under pressure; a series of spaced metal plates so disposed in relation to said outlet opening that the spray medium must pass between them in moving from said chamber toward said cylinder; means for placing an electrical charge on said plates to cause precipitation of a controlled quantity of the charged particles of said dampening spray medium; means for placing an electrical charge on said spray medium; and means for varying the strength of the electrical charge of a given polarity on said plates with respect to the charge on said spray medium.

3. A spray dampening system for lithographic ofiset presses comprising: an elongated chamber arrangeable in proximity to a printing cylinder adapted to carry a printing plate or medium to be dampened and having an outlet opening therein opposite said cylinder; means for providing in said chamber an electrically-charged dampening spray medium under pressure; a series of metal plates so disposed in relation to said outlet opening that the spray medium must pass between them in moving from said chamber toward said cylinder; means for placing an electrical charge on said plates to cause precipitation of a controlled quantity of the charged particles of said dampening spray medium; means for placing an electrical charge on said spray medium; means for varying the strength of the electrical charge of a given polarity on said plates with respect to the charge on said spray medium; and means controlled by the speed of the press for automaticallyregulating the spray to cause the amount thereof to increase or decrease with increase or decrease in the speed of the press.

4. A spray dampening system for lithographic offset presses comprising: an elongated chamber arrangeable in proximity to a printing cylinder adapted to carry a printing plate or medium to be dampened and having an outlet opening therein opposite said cylinder; means for providing in said chamber an electrically-charged dampening spray medium under pressure; a series of metal plates so disposed in relation to said outlet opening that the spray medium must pass between them in moving from said chamber toward said cylinder;'means for placing an electrical charge on said plates to cause precipitation of a controlled quantity of the charged particles of said dampening spray medium; means for placing an electrical charge on said spray medium; means for varying the strength of the electrical charge of a given polarity on said plates with respect to the charge on said spray medium; and means controlled by the speed of the press for automatically regulating the spray to cause the amount thereof to increase or decrease with increase or decrease in the press speed while the pressure in the chamber remains substantially constant.

5. A spray dampening system for lithographic ofiset presses comprising: an elongated chamber arrangeable' in proximity to a printing cylinder (having the customary cylinder gap) adapted to carry a printing plate or medium to be dampened and having an outlet opening therein opposite said cylinder; means for providing in said chamber an electrically-charged dampening spray medium under pressure; a series of metal plates so disposed in relation to said outlet opening that the spray medium must pass between them in moving from said chamber toward said cylinder; means for placing an electrical charge on said plates to cause precipitation of a controlled quantity of the charged particles of said dampening spray medium; means for placing an electrical charge on said spray medium; means for varying the strength of the electrical charge of a given polarity on said plates with respect to the charge on said spray medium; electrical means including a switch and voltage control means for increasing the voltage on said plates when said cylinder gap is opposite the spray area to thereby cause substantially complete precipitation of the spray on the plates and thus cut off said spray; and a rotating element on said press for controlling said last mentioned means.

6. A spray dampening system for lithographic oflFset presses comprising: an elongated chamber arrangeable in proximity to a printing cylinder adapted to carry a printing plate or medium to be dampened and having a lengthwise slot therein opening toward said cylinder; means for providing in said chamber an electricallycharged dampening spray medium under pressure; a series of metal plates so disposed in relation to said outlet opening that the spray medium must pass between them in moving from said chamber toward said cylinder, said plates being arranged in sets lengthwise of the chamber with the sets insulated from each other; means for placing an electrical charge on said plates to cause precipitation of a controlled quantity of the charged particles of said dampening spray medium, said means including devices whereby the charge on different sets of the plates may be varied with the pressure on the spray medium passing through all said sets of plates remaining substantially constant; means for placing anelectrical charge on said spray medium; and means for varying the strength of the electrical charge of a given polarity on said plates with respect to the charge on said spray medium.

References Cited in the file of this patent UNITED STATES PATENTS 2,287,837 Smyser June 30, 1942 2,586,480 Ras Feb. 19, 1952 2,590,429 Ras Mar. 25, 1952 

